The-present invention relates to a power assist apparatus that includes a manipulator that holds loads at its tip and a mobile base on which the manipulator is mounted, which assists human operators to carry loads by amplifying an operational force applied to the manipulator, and to a method of controlling the power assist apparatus.
Research into power assist methods in which humans and robots cooperate to carry loads has been carried out in the U.S., at the University of California, and in Japan, at Tohoku University, the Mechanical Engineering Laboratory, and elsewhere. These methods involve using two force sensors to sense a load being manipulated at the tip of a robot manipulator, and an operational force applied by an operator. An operational force applied to the manipulator by the operator is amplified and applied to the load, making it easier for the human operator to move the load.
If the base of the manipulator is supported on a fixed base, loads can only be handled within the range of the robot arm movement. Mounting the manipulator on a mobile base increases the range over which the manipulator can be used to handle loads. However, when the manipulator is mounted on a mobile base, it becomes necessary to use a method of cooperatively controlling the manipulator and the mobile base to maintain the stability of the base. When the manipulator is mounted on the mobile base, there is a risk that some manipulator positions and loads may cause the base to fall over. To avoid this, the tip position of the manipulator relative to the base must be controlled.
In one prior art for cooperative control method, a system that combines the mobile base and manipulator is controlled as a redundant system in which the position of the mobile base is constantly adjusted in accordance with manipulator operations. However, the base with the manipulator weighs a considerable amount, and having such a heavy machine constantly moving around in the vicinity of humans during work operations is undesirable from the standpoint of safety. Moreover, this continuous movement also consumes much energy, and also reduces the response speed off the manipulator.
In view of the above circumstances, an object of the present invention is to provide a power assist apparatus that is safe during work operation, keeps down energy consumption and provides improved manipulator response speed, and a control method for controlling the apparatus.
To attain the above object, the present invention provides a power assist apparatus comprising: a manipulator that holds a load at its tip; an autonomously mobile base on which the manipulator is mounted; and control means that, when the manipulator tip is within a prescribed operating region relative to the mobile base, maintains the mobile base in a stationary state, and when the manipulator tip moves outside said operating region, moves the mobile to decrease distance between the mobile base and the manipulator tip; said power assist apparatus assisting with carrying of loads by amplifying an operational force applied to the manipulator.
The above power assist apparatus further comprises the of resistance imparting means that, when the tip of the manipulator is within a prescribed peripheral region in proximity to a perimeter within the operating region, operates the manipulator with a resistance force applied to an applied operational force.
It is preferable that the resistance force imparting means operates the manipulator with a resistance force that is gradually increased as the tip of the manipulator moves further toward the outer perimeter of the peripheral region provided in the operating region. More preferably, the resistance force applied by the resistance imparting means increases in accordance with a non-linear spring coefficient. When the mobile base is autonomously mobile, it is preferable for the manipulator to be operated so that the resistance force is gradually reduced as the distance separating the manipulator tip and the mobile base decreases and, when the distance between the mobile base and the manipulator tip has reached a prescribed initial state, for the resistance force to be at zero.
The object is also attained by a control method for controlling a power assist apparatus that comprises a manipulator that at a tip thereof holds loads to be moved and an autonomously mobile base on which the manipulator is mounted and assists with handling of loads by amplifying an operational force applied to the manipulator, said method comprising: maintaining the mobile case in a stationary state when the manipulator tip is within a prescribed operating region relative to the mobile base; and moving the mobile base to decrease a distance between the mobile base and the manipulator tip when the manipulator tip moves outside said operating region.
In accordance with the control method, when the tip of the manipulator is within a prescribed peripheral region in proximity to a perimeter within the operating region, the manipulator is operated with a resistance force being applied to an applied operational force.
Moreover, it is preferable that the resistance force imparting means operates the manipulator such that the resistance force is gradually increased as the manipulator moves toward the outer perimeter within the peripheral region provided in the operating region. More preferably the resistance force applied by the resistance imparting means increases in accordance with a non-linear spring coefficient. When the mobile base is autonomously mobile it is preferable for the manipulator to be operated so that the resistance force is gradually reduced as the distance separating the manipulator tip and the mobile base decreases and, when the distance between the mobile base and the manipulator tip has reached a prescribed initial state, for the resistance force to be at zero.
Thus, in accordance with this invention, as described above, the mobile base is moved only when the tip of the manipulator reaches the outer periphery of the operating region, which, in addition to being advantageous in terms of safety, is also advantageous in terms of energy consumption and the response characteristics of the manipulator. Furthermore, when the mobile base is autonomously mobile, the frequency of mobile base movements can be decreased by retracting the manipulator tip to its initial position enhancing the above effects.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.